Calcium homeostasis during magnesium treatment in aneurysmal subarachnoid hemorrhage

Objective Magnesium treatment in patients with subarachnoid hemorrhage (SAH) can result in hypocalcemia; this hypocalcemia increases the risk of delayed cerebral ischemia (DCI) and poor outcome. We assessed whether low serum levels of total calcium in patients with SAH treated with magnesium is mediated by parathyroid hormone (PTH) or calcitriol, and whether increased PTH or low serum levels of ionized calcium are associated with an increased risk of DCI and poor outcome. Patients and Methods We studied 167 patients included in a randomized, placebo controlled trial on magnesium in SAH. Mean serum magnesium during treatment was related to mean serum levels of ionized calcium, PTH and calcitriol with linear regression. Hypocalcemia (Ca(2+)) and high serum PTH were related to the occurrence of DCI by means of the Cox proportional hazards model and to poor outcome by logistic regression. Results Serum magnesium was inversely related to ionized calcium (B = -0.1; 95% CI -0.12 to -0.06), but not to PTH or calcitriol. Neither hypocalcemia nor high serum PTH was related to DCI. Hypocalcemia did not increased the risk for poor outcome (OR 1.2; 95% CI 0.6-2.3). In the subgroup of patients with known PTH (n = 67), high serum PTH increased the risk for poor outcome (OR 5.4; 1.6-18.9). Conclusions Magnesium treatment in patients with SAH leads to hypocalcemia without effect on outcome. PTH is related to poor outcome, but this is independent of magnesium therapy